Water-insoluble hydrogels are polymeric materials which are c le of absorbing large quantities of fluids such as water and body wastes and which are further capable of retaining such absorbed fluids under moderate pressures. These absorption characteristics of water-insoluble hydrogels make such materials especially useful for incorporation into absorbent articles such as disposable diapers. Harper et al.; U.S. Pat. No. 3,669,103; Issued June 13, 1972 and Harmon; U.S Pat. No. 3,670,731; Issued June 20, 1972, for example, both disclose the use of hydrogel, i.e., "hydrocolloid," materials in absorbent products.
The effectiveness of fluid-absorbing hydrogel materials in disposable absorbent articles can be quite dependent upon the form, position and/or manner in which the hydrogel material is incorporated into the absorbent article. In some cases, for example, the effectiveness of hydrogel fluid absorption in absorbent articles can be adversely affected by a phenomenon called gel blocking. The term gel blocking describes a situation that occurs when a hydrogel particle, film, fiber, composite, etc. is wetted. Upon wetting, the surface of the hydrogel material swells and inhibits liquid transmission to the interior of the absorbent material. Wetting of the interior subsequently takes place via a very slow diffusion process. In practical terms, this means that absorption of fluid by the article is much slower than discharge of fluid to be absorbed, and failure of a diaper or sanitary napkin or other absorbent article may take place well before the hydrogel material in the absorbent article is fully saturated.
A number of prior art attempts have been made to improve the effectiveness of hydrogel materials in absorbent articles by minimizing gel blocking tendency. Thus, for Procter & Gamble; European Patent Application EP-A-No. 122,042; Published Oct. 17, 1984 discloses absorbent structures wherein hydrogel particles are dispersed in an air-laid web of hydrophilic fibers compressed to a particular density. Mesek et al.; U.S. Pat. No. 4,235,237; Issued Nov. 25, 1980 discloses an open absorbent network having particles of water-insoluble, water-swellable material spaced from each other within the network. Mazurak et al; U.S. Pat. No. 4,381,782; Issued May 3, 1983 discloses absorbent fibrous structures containing mixtures of hydrogel particles and surfactant-treated filler materials. Colgate Palmolive; U.K. Patent Specification No. 2,132,897A; Published July 18, 1984 discloses disposable absorbent articles containing a pad assembly having one or more surfaces coated with absorbent polymer in patterns designed to prevent gel blocking.
Other prior art attempts to improve the effectiveness of hydrogel materials in absorbent structures have involved particular arrangements for positioning hydrogel within the absorbent structure in discrete zones such as layers or pockets. The aforementioned EP-A-No. 122,042, for example, indicates that a hydrogel-containing absorbent structure can be positioned as a lower layer in a disposable absorbent product underneath an upper layer containing only hydrophilic fiber material. Mesek et al.; U.S. Pat. No. 4,102,340; Issued July 25, 1978 discloses an absorbent article having a hydrogel-containing batt positioned underneath a densified layer of fibrous material. Elias; U.S. Pat. No. 4,381,783; Issued May 3, 1983 discloses an absorbent article which includes an absorbent layer containing pockets of an admixture of hydrogel particles and discrete introfying particles. Holtman et al., U.S. Pat. No. 4,333,426; Issued June 8, 1982 and Holtman; U.S. Pat. No. 4,333,463; Issued June 8, 1982 both disclose absorbent structures containing reservoirs of superabsorbent particles positioned near one end of the structure at the void zone of the wearer. Personal Products Co.; European Patent Application EP-A-No. 108,637; Published May 16, 1984 describes thin absorbent products having a superabsorbent-containing absorbing layer and a wicking layer. Willington; U.K. Patent Specification No. 1,406,615; Published Mar. 15, 1973 discloses an absorbent pad having a urine-gelling agent incorporated only in the part of the pad "where it will be most effective."
Notwithstanding the various prior art attempts to improve the effectiveness of hydrogel materials in absorbent structures and products, there is a continuing need to identify hydrogel-containing absorbent articles wherein the hydrogel material is especially effective and efficient in performing its intended function of holding discharged body fluids without interfering with the acquisition and distribution of body fluids by and within the article. Hydrogel materials are generally significantly more expensive than readily available hydrophilic fiber materials (e.g. cellulose fibers). Accordingly it would be advantageous to provide articles wherein either absorbent capacity of the hydrogel-containing article can be improved or wherein a given absorbent capacity of an article can be maintained while reducing the amount of relatively expensive hydrogel material used. It would also be advantageous to provide articles wherein the fluid-storing hydrogel material does not adversely affect the ability of the absorbent article to quickly acquire discharged body fluids. It is therefore a primary objective of the present invention to provide absorbent articles which are especially effective and efficient in their use of hydrogel absorbent materials.
Another potential advantage which can be provided by certain hydrogel-containing disposable absorbent articles relates to the prevention or reduction of diaper rash. Diaper rash is a common form of irritation and inflammation of those parts of an infant's skin normally covered by a diaper. This condition is also referred to as diaper dermatitis, napkin dermatitis, napkin rash or nappy rash.
It is generally accepted that true "diaper rash" or "diaper dermatitis" is a condition which is commonly, in its most simple stages, a contact irritant dermatitis. The irritation of simple diaper rash results from extended contact of the skin with body waste. Diapers which catch and hold body waste in contact with the skin for long periods of time thus cause and/or aggravate diaper rash.
It has now been discovered that a primary cause of diaper rash is a particular set of conditions which arises as a result of prolonged contact of skin with mixtures of feces and urine. Activity of proteolytic and lipolytic fecal enzymes present in such a mixture is believed to be a major factor in producing skin irritation. Urine in contact with enzymes from feces can also result in production of ammonia which raises skin pH. This rise in skin pH, for example to levels of 6.0 and above, in turn increases that fecal proteolytic and lipolytic enzymatic activity which produces diaper rash.
The foregoing diaper rash model suggests that effective diaper rash control may be achieved by preventing mixtures of urine and feces from contacting diapered skin for any significant length of time. Prior art disposable diaper structures have not in general been designed to eliminate mixing of discharged urine and feces. It is, accordingly, a secondary objective of the present invention to provide absorbent articles such as diapers which hold discharged urine and feces in separate locations within the absorbent article and which might thereby prevent or reduce diaper rash caused by skin contact with urine-feces mixtures.